This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. Primary support for the subproject and the subproject's principal investigator may have been provided by other sources, including other NIH sources. The Total Cost listed for the subproject likely represents the estimated amount of Center infrastructure utilized by the subproject, not direct funding provided by the NCRR grant to the subproject or subproject staff. We are requesting beam time to further on-[unreadable]going projects in the laboratories of four PIs. These projects include (1) Structural studies of proteins involved in nitric oxide signaling, with emphasis on soluble guanylate cyclase (sGC), its functional domains and its regulatory partners. Several sGC fragments have been expressed and small crystals obtained for two of these. Two model systems, nitrophorin 4(Rhodnius prolixus) and thioredoxin (human)are under study for understanding nitrosyl heme and S-[unreadable]nitrosocysteine chemical biology. Crystals of these proteins diffract past 1.[unreadable].(2)Structures of proteins involved in copper transport and homeostasis(McEvoy);(3) Evolution of Cro and lipocalin proteins (Cordes), and (4) Structure/mechanism studies of QueD,(Bandarian)Crystals are available for all projects. Synchrotron radiation is needed for(1)MAD structure determination, (2) to provide sufficient resolution to determine accurate geometrical parameters such as heme distortion, metal binding site geometry and S-nitrosothiol geometry;(3) to provide variable wavelength x-[unreadable]rays for unambiguous identification of bound metal atoms and (4)to control photoreduction of metal sites and S-[unreadable]NO bonds.